Method for producing multiaxial warp knit fabric

ABSTRACT

A method for producing multiaxial warp knit fabrics with extended threads in longitudinal, transverse and diagonal directions as a result of direct insertion of the diagonal threads as weft sections onto backs of rising needles of needle bars. The method includes simultaneously inserting at least two diagonal thread systems contrarily as part wefts for each needle bar on a right/right warp knitting machine.

PRIORITY CLAIM

This is a U.S. national stage of application No. PCT/CH00/00316, filedon Jun. 9, 2000. Priority is claimed on that application and on thefollowing application: Country: Germany, Application No: 199 28 635.3,Filed: Jun. 23, 1999.

BACKGROUND OF THE INVENTION

The production of multiaxial warp knit fabrics by the incorporation ofreinforcing threads as weft, warp and diagonal threads is already known.DE-A 33 04 345 describes, for example, a warp knit cloth with a normalwarp knit fabric as the cloth ground and with reinforcing threadsinserted into the latter. Weft threads run parallel to one another andare arranged in each case between two stitch heads of successive stitchrows and, in addition, two sets of diagonal threads are provided, whichin each case run alternately between two stitch heads of stitch rowssucceeding one another in the knitting direction. In this version, thereare in the warp, weft and diagonal directions reinforcing threads whichare not pricked through by the knitting needles. All the reinforcingthreads are arranged at an angle of 45° to one another, which, however,as a consequence of the method cannot be modified.

1. Technical Field

The invention relates to a method for the production of multiaxial warpknit fabrics with extended threads in the longitudinal, transverse anddiagonal directions as a result of the direct insertion of the diagonalthreads as weft sections onto the backs of the rising needles. Thetextile structures produced by the method are used, by virtue of theirhigh stability and strength in the various directions, as reinforcementin composite materials, for example in automobile construction, railvehicle construction and the aeronautic industry.

2. Prior Art

The production of multiaxial warp knit fabrics by the incorporation ofreinforcing threads as weft, warp and diagonal threads is already known.DE-A 33 04 345 describes, for example, a warp knit cloth with a normalwarp knit fabric as the cloth ground and with reinforcing threadsinserted into the latter, in which weft threads run parallel to oneanother and are arranged in each case between two stitch heads ofsuccessive stitch rows and, in addition, two sets of diagonal threadsare provided, which in each case run alternately between two stitchheads of stitch rows succeeding one another in the knitting direction.In this version, there are in the warp, weft and diagonal directionsreinforcing threads which are not pricked through by the knittingneedles. All the reinforcing threads are arranged at an angle of 45° toone another, which, however, as a consequence of the method cannot bemodified.

A special warp knitting machine for the processing of multiaxialcontextures is also known, in which up to seven thread plies aresuspended in a transport chain (90°/±diagonal/90°/−diagonal/90°/+diagonal/90°) and are consolidated in theregion of the knitting point by means of a warp knit weave. A 0° threadsystem may be laid in place as the last thread ply directly in front ofthe knitting point. However, the knitting operation makes it necessaryto prick through the closely layered thread plies, thus leading to thedisplacement of the threads. The consequences of this are a reduction inthe cloth strength and an uneven defective structure density (MelliandTextile Reports 11/86, pages 804 to 806).

By means of the stitch-bonding machine, Malimo type, with multiaxialweft insertion, it is possible to produce multiaxial knit fabrics, forexample with a thread ply combination of 0°/−90°/−45°/−90°/±45° in thecase of angular deviations of 1 to 5°, that is to say the weft threadsare not exactly parallel (Kettenwirk-praxis [Warp Knitting Practice]2/94, pages 15 to 17).

In the multiaxial knitting technique for the production of industrialtextiles on a right/left flat knitting machine, the multiaxial threadinsertion is carried out by means of a combination of threads in thedirections 0°/90°/±45° (ITB Vliesstoffe—technische Textilien [ITBnonwoven textiles] 1/95, pages 44 to 45). The particular feature of thisknitted fabric is that the threads running diagonally and vertically(0°) alternate after every second row on the front side and rear side ofthe cloth. The thread run for the warp threads and diagonal threads fromthe front side to the rear side of the sheetlike structure isimplemented by additional drives for the feed elements, one forcontrolling the crossing movement and one for controlling the rackingmovement, which is executed it a revolving manner. This tying-intechnique is intended primarily to prevent the delamination which occursit the case of composite materials.

A biaxial knitting technique and a biaxially reinforces multiply knittedfabric are known from DE 49 19 985 A1. Altogether five weft systems canbe inserted at right angles with crossing (90°/0°/90°/0°/90°) on aright/right flat knitting machine. Due to the arrangement of the threadplies (0°/°90°), it is not possible to produce multiaxial knittedfabrics. Moreover, the 0° thread plies are pricked through by theemerging needles, thus leading to the same disadvantages as in thespecial warp knitting machine.

Furthermore, several patent specifications (DD 268 720, DD 268 721, DD258 722, DD 268 723, DD 268 729, DD 256 885) disclose variants for theproduction of multiaxial devices, in particular for stitch-bondingmachines, by means of which an improvement in the quality of multiaxialsheetlike structures at a reduced mechanical outlay and a variableconfiguration due to the feed of finite thread sections from threadstorage cartridges are to be achieved.

In the techniques which work on the basis of presented thread groups, asa consequence of the principle the 0° thread plies always form thecovering layer, with the result that the isotropy of the compositestructure is impaired in the case of the multiply structures to beachieved. Some of the known multiaxial structures possess thread systemscrossing at right angles, which cannot satisfy the requirements as tofiber angles (no greater than 45°) the known devices for the insertionof thread groups into transport chains make it possible to vary theguide angle of the diagonal threads within certain limits, but not whenthe machine is running.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for theproduction of knitted reinforcing structures with a multiple variablemultiaxial thread run, by means of which the thread angle can be changedas a function of the required force line runs, with the machine running,in the region of the diagonal and 90° threads. At the same time, thepricking through of thread plies or the pricking on of threads is to beavoided, in order to ensure cost-effective production.

Pursuant to this object, and others which will become apparenthereafter, one aspect of the present invention resides in a method forthe production of multiaxial warp knit fabrics with extended threads inthe longitudinal, transverse and diagonal directions as a result of thedirect insertion of the diagonal threads as weft sections onto the backsof the rising needles of the needle bars. At least two diagonal threadsystems are simultaneously inserted contrarily as part wefts for eachneedle bar on a right/right warp knitting machine.

In another embodiment, 0° threads are inserted as upright wefts betweenthe diagonal thread systems.

In yet another embodiment of the invention 90° threads aresimultaneously inserted as through wefts in line with the stitch rows.The 90° threads, in still a further embodiment, are partiallydiscontinued or continue to operate as a part weft.

In an additional embodiment of the invention 0° threads are additionallyrun in, and are racked laterally at a distance from one another.

In still another embodiment, the diagonal threads are discontinuedaccording to the pattern and run as 0° threads.

The advantages achieved by nears of the invention are, in particular,that, by means of the right/right warp knitting machine, weft insertionin line with the stitch rows can take place, while, due to thesimultaneous contrary insertion of the diagonal threads on the front andrear needle bar, four diagonal thread systems for each complete stitchrow can be tied in at a low outlay. Another advantage is that the 0°threads are fed and tied in directly between the contrarily moved weftthreads. The pricking through of the threads is ruled out in thisprocedure, so that a better utilization of substance is possible, ascompared with multiaxially knitted contextures. By virtue of the directweft insertion, there is no need for a prior production of thecontexture (suspension of the thread groups inserted at an angle in thetransport chains), so that there is a direct control of the rackingdistance of the weft threads in the region of the knitting zone. It isthereby possible to change the guide angle of the diagonal threadsaccording to the force lines. 90° threads may likewise be brought, asdesired, into a 0° position, with the result that differentiated layerthicknesses can be produced in a varying sequence.

Moreover, by means of the tying elements of a coarse three-dimensionalright/right warp knit structure, the multiaxially layered threads aresubstantially reinforced in the z-direction and consequently theresistance to delamination is improved considerably.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is illustrated in the drawingand is described in more detail below. In the drawing:

FIG. 1 shows a diagrammatic illustration of the knitting point of aright/right warp knitting machine for carrying out the method accordingto the invention,

FIG. 2 shows a section through a right/right warp knit fabric accordingto FIG. 1,

FIG. 3 shows a diagrammatic illustration of a top view of theright/right warp knit fabric according to the detail in FIG. 2

PREFERRED EMBODIMENTS

According to the section illustrated in FIG. 1, the knitting point of aright/right warp knitting machine is formed by a front and rear needlebar 1, 1′ with knitting needles and with the associated knockover edges2, 2′ and the thread guide members. The thread guide members consist ofat least one oscillating ground guide rail 3, which carries outinsertion for stitch formation 3′, 3″ on the front and rear needle bar1, 1′, and of at least one oscillating weft guide rail 4, 5, which isassigned to the front and rear needle bar 1, 1′ and via which additional0° weft threads (4′, 5′) run in, which, if required, are rackedlaterally. The thread guide members consist, furthermore, ofnonoscillating thread guides 6 to 13. The thread guide 6 is assigned tothe front needle bar 1 and inserts a 90° thread system 6′ which is tiedoff in the region of the front needle bar 1 by the ground threads 3′ bymeans of the guide rail 3. The thread guide 6 tray also be discontinuedor may guide only over part distances, depending on the force line run.The thread guides 7 and 9 are provided for the insertion of diagonalthreads 7′, 9′ and are designed, for example, as small tubes and arearranged on an oscillating or rotating driving device, at the spacing ofthe needle division, over the entire working width. After the respectivecloth edge has been reached, the thread guides 7 travel into theposition of the thread guides 9 and the thread guides 9 travel into theposition of the thread guides 7. In this case, the racking length foreach stitch row depends on the desired insertion angle of the diagonalthreads 7′, 9′. If required, the diagonal threads 7′, 9′ may also bediscontinued according to the pattern and run as 0° threads.

The rigidly arranged thread guide 8 is provided for feeding the 0°threads 8′ which lie between the diagonal threads 7′ and 9′ in the knitfabric. The thread guides 10 to 13 are assigned to the rear needle bar1′. The rear diagonal threads 10′ and 12′ are inserted by the threadguides 10 and 12, the insertion principle corresponding to that of thethread guides 7 and 9.

The rear 0° threads 11′ are inserted between the diagonal threads 10′and 12′ by rigidly arranged thread guides 11 in a similar way to thethreads 8′. The thread guide 13 inserts the rear 90° thread system 13′,while, as in the case of the thread guide 6, discontinuation orinsertion over part distances may also take place.

The method according to the invention results, according to FIG. 2, inthe following arrangement of the thread plies in the knit fabric: 90°;−diagonal; 0°; +diagonal; 0° with racking according to the pattern; 0°with racking according to the pattern; −diagonal; 0°; −diagonal; 90°.The insertion angles of the diagonal threads 7′ and 9′ or 10′ and 12′can be modified by the lengthening or shortening of the underlay lengthfor each stitch row.

FIG. 3 illustrates z crossing point of four thread systems 6′, 7′, 8′and 9′ on the front needle bar 1 . Accordingly, the 90° threads 6′ liein front of the diagonal threads 7′ and 9′ and the 0° threads 8′ runbetween the diagonal threads 7 ′, 9′.

The 90° threads, diagonal threads and 0° threads are arranged in asimilar way on the rear needle bar 1′ having the thread systems 10′,11′, 12′ and 13′, the crossing points of the front thread systems and ofthe rear thread systems being arranged so as to be offset to one anotheraccording to the right/right knit fabric structure.

By means of the method according to the invention, multiaxial structureswith a specific force line run in all directions can be producedoptimally for a multiplicity of fields of use.

What is claimed is:
 1. A method for producing multiaxial warp knitfabrics with extended threads in longitudinal, transverse and diagonaldirections as a result of direct insertion of the diagonal threads asweft sections onto backs of rising needles of needle bars, comprisingthe step of simultaneously inserting at least two diagonal threadsystems oppositely as part wefts for each needle bar on a right/rightwarp knitting machine.
 2. A method according to claim 1, includinginserting 0° threads as upright wefts between the diagonal threadsystems.
 3. A method according to claim 1, including simultaneouslyinserting 90° threads as through wefts in line with the stitch rows. 4.A method according to claim 3, wherein the 90° threads are partiallydiscontinued to form a part weft.
 5. A method according to claim 3,wherein the 90° threads continue to operate as a part weft.
 6. A methodaccording to claim 1, further including additionally running in 0°threads which are racked laterally at a distance from one another.
 7. Amethod according to claim 1, including discontinuing the diagonalthreads according to a pattern and running the diagonal threads as 0°threads.